As a light condensing and heat collecting device used for solar thermal power generation, a device including a solar light reflecting plate that condenses solar light and a heat collecting tube that is disposed at the focal point of the solar light reflecting plate is known.
As the solar light reflecting plate (reflecting mirror) provided in the light condensing and heat collecting device, for example, JP 57-4003 A discloses a solar light reflecting plate including a substrate 4 formed of an appropriate material, for example, metal and alloy such as aluminium, steel plate and stainless steel, or plastic, or the like, a metallic reflective film 5 formed of aluminium, silver, or the like and deposited on the substrate 4, and a transparent inorganic protective film 6 formed of a vitreous film such as SiO and SiO2 and deposited on the surface of the metallic reflective film 5 (refer to the upper-right column of page 2).
As disclosed in JP 57-4003 A, in a case where the solar light reflecting plate (reflecting mirror) is provided with a reflective film, a diffuse reflectance is improved, but a regular reflectance that is important in solar thermal power generation is lowered.
We found that the regular reflectance is improved by reducing the surface roughness of the outermost surface (the surface of the reflective film) of the solar light reflecting plate.
However, it became clear that a high regular reflectance does not necessarily secure a high light condensing property and an improved power generation efficiency.
Thus, it could be helpful to provide a solar light reflecting plate and a light condensing and heat collecting device capable of obtaining an excellent light condensing property.